Continued from page 1
Installment 3
PHP Session Handling - Cookies Enabled
Instead of storing session information at
browser through use of cookies, information can instead be stored at server in session files. One session file is created and maintained for each user session. For example, if there are three concurrent users browsing website, three session files will be created and maintained - one for each user. The session files are deleted if session is explicitly closed by PHP script or by a daemon garbage collection process provided by PHP. Good programming practice would call for sessions to be closed explicitly in script.
The following is a typical server-browser sequence of events that occur when a PHP session handling is used: 1. The server knows that it needs to remember State of browsing session 2. PHP generates a sssion ID and creates a session file to store future information as required by subsequent pages 3. A cookie is generated wih session ID at browser 4. This cookie that stores session ID is transparently and automatically sent to server for all subsequent requests to server
The following PHP session-handling example accomplishes same outcome as previous cookie example. Copy code below (both php and html) into a file with .php extension and test it out.
[?php //starts a session session_start();
//informs PHP that count information needs to be remembered in session file if (!session_is_registered("count")) { session_register("count"); $count = 0; } else { $count++; }
$session_id = session_id(); ?]
[html] [head] [title]PHP Session Handling - Cookie-Enabled[/title] [/head] [body] The current session id is: [?=$session_id ?] This page has been displayed: [?=$count ?] times. [/body] [/html]
A summary of functions that PHP provides for session handling are: 1. boolean start_session() - initializes a session 2. string session_id([string id]) - either returns current session id or specify session id to be used when session is created 3. boolean session_register(mixed name [, mixed ...]) - registers variables to be stored in session file. Each parameter passed in function is a separate variable 4. boolean session_is_registered(string variable_name) - checks if a variable has been previously registered to be stored in session file 5. session_unregister(string varriable_name) - unregisters a variable from session file. Unregistered variables are no longer valid for reference in session. 6. session_unset() - unsets all session variables. It is important to note that all variables remain registered. 7. boolean session_destroy() - destroys session. This is opposite of start_session function.
The next installment discusses how to manage sessions using PHP session handling functions when cookies are disabled...
Installment 4
PHP Session Handling - Without Cookies
If cookies are disabled at browser, above example cannot work. This is because although session file that stores all variables is kept at server, a cookie is still needed at browser to store session ID that is used to identify session and its associated session file. The most common way around this would be to explicitly pass session ID back to server from browser as a query parameter in URL.
For example, PHP script generates requests subsequent to start_session call in following format: http://www.yourhost.com/yourphpfile.php?PHPSESSID=[actual session ID]
The following are excerpts that illustrate discussion:
Manually building URL: $url = "http://www.yoursite.com/yourphppage.php?PHPSESSID=" . session_id(); [a href="[?=$url ?]" rel="nofollow"]Anchor Text[/a]
Building URL using SID: [a href="http://www.yoursite.com/yourphppage.php?[?=SID ?]" rel="nofollow"]Anchor Text[/a]
This PHP scripting article is written by John L. John L is the Webmaster of The Ultimate BMW Blog! (http://www.bimmercenter.com).
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